Apparatus and methods for continuously electrocoating metal blanks and/or coiled metal substrates

ABSTRACT

A continuous electrocoat apparatus is provided for applying a coating onto a substantially flat substrate, e.g., an electroconductive substrate in coil or blank form. In one embodiment, the apparatus includes a first electrocoat tank having a coating region and a non-conductive conveyor extending at least partially into the first electrocoat tank and defining a conveyor path. A plurality of electrically conductive supports are carried on the conveyor. A connecting system is configured to selectively place at least a portion of the supports in electrical contact with an electrical power source when the selected supports are in the coating region of the first electrocoat tank.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is related to U.S. patent application Ser. No.______, entitled “Process for Electrocoating Metal Blanks and CoiledMetal Substrates” of Donald Emmonds et al. and filed concurrentlyherewith, which related application is herein incorporated by referencein its entirety.

[0002] 1. Field of the Invention

[0003] The present invention relates generally to electrodepositionapparatus and methods and, more particularly, to apparatus and methodsfor continuously electrocoating a metal substrate in blank or coil form.

[0004] 2. Technical Considerations

[0005] Throughout many industrial fields, metal substrates are coated,cut, and treated to form a variety of metal parts.

[0006] For example, in the fields of appliance fabrication andautomotive fabrication, metal substrates in the form of metal coils areprocessed and shaped into blanks. The term “blank” conventionally refersto a flat or substantially flat metal piece, e.g., a metal piece shearedfrom a coil, which has been cut to form a particular flat shape. Theflat blanks are shaped or pressed into three-dimensional parts, such asfront and side panels for appliances, e.g., refrigerators, washers anddryers, metal office furniture, e.g., filing cabinets and desks, andarchitectural products, e.g., fluorescent lighting fixtures.

[0007] In the past, such metal blanks were typically “post-painted”,i.e. first shaped by bending, welding, pressing, etc. into a finalthree-dimensional form before applying a coating to prevent damaging thecoating during the shaping process. The coating could be applied to theshaped part by wet-painting, powder painting, or electrocoatingtechniques. In a typical wet-painting process, a solvent-borne coatingis applied to the shaped part, e.g., by spraying or rolling and thencured. However, increasingly stringent environmental regulations makestorage and disposal of coating solvents, particularly volatile organiccompounds, more expensive and the cure times for these solvent-bornecoatings are relatively long. Further, such wet-painting techniques aretypically wasteful of the coating composition and only allow theapplication of a very thin coating thickness. In a powder coatingprocess, an electrostatically charged powder coating composition havingonly a fraction of the volatile solvents associated with wet paints isapplied onto the metal part, e.g., by spraying, and then heated to meltand cure the coating through a crosslinking process. This technique isalso wasteful of the coating composition. In electrocoating techniques,a coating is applied onto a conductive substrate under the influence ofan applied electrical potential. Electrocoating generally offersincreased paint utilization and lower environmental contamination. Whilegenerally acceptable for producing coated parts, “post-painting” ismanpower and time intensive and typically requires a separate paintingfacility. Additionally, the formed or shaped three dimensional parts aremore difficult to store and transport than the flat blanks from whichthey are formed.

[0008] In order to reduce the storage and transport drawbacks ofpost-painting the blanks, “pre-painting” techniques for coating thecoils or blanks by wet painting or powder painting processes prior toshaping were developed Examples of wet painting processes are disclosedin U.S. Pat. Nos. 3,887,720 and 5,271,144. Examples of powder paintingprocesses are disclosed in U.S. Pat. Nos. 4,104,416; 5,264,254; and5,439,704. For Example, U.S. Pat. No. 5,439,704 teaches a combined coiland blank powder coating line in which, due to the necessity of placingthe blanks on a horizontal support surface for transport, only thetopside of the blank can be powder coated, thus leaving the undersideuncoated.

[0009] While these wet and powder pre-painting processes provideadvantages over the previous post-painting procedures, e.g., moreadvantageous storage and transport, they are, nonetheless, typicallywasteful of the coating material, e.g., due to overspray, and areenvironmentally unfriendly. To date, no electrodeposition pre-paintingmethods have proved commercially viable, e.g., have not provedcommercially acceptable and/or have not produced electrodepositedcoatings mar resistant and flexible enough to withstand the stressesinvolved during the subsequent shaping process without fracturing orlosing adhesion of the coating.

[0010] It would be advantageous to provide an apparatus and/or methodfor electrocoating, e.g., pre-painting, one or more coatings onto ablank or coil metal substrate to provide efficient paint utilization andfaster cure times while also providing sufficient durability andflexibility to withstand post coating shaping of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a side, schematic view (not to scale) of an exemplaryelectrocoating apparatus incorporating features of the invention;

[0012]FIG. 2 is a sectional view of the electrocoating apparatus of FIG.1 taken along the line II-II;

[0013]FIG. 3 is an enlarged view of an exemplary connecting system ofthe electrocoating apparatus shown in FIG. 1; and

[0014]FIG. 4 is a flow chart of an exemplary electrocoating methodincorporating features of the invention.

SUMMARY OF THE INVENTION

[0015] A continuous electrocoat apparatus is provided for applying acoating onto at least a portion of a substantially flat substrate havingtwo major surfaces. The apparatus comprises a first electrocoat tankwith at least one first electrode spaced from at least one secondelectrode and defining a first coating region to apply a first aqueouselectrodepositable coating composition onto both major surfaces of thesubstrate between the first and second electrodes. The apparatus furtherincludes a second electrocoat tank located downstream of the firstelectrocoat tank with at least one third electrode located in the secondelectrocoat tank and defining a second coating region adjacent the thirdelectrode to apply a second aqueous electrodepositable coatingcomposition onto substantially one major surface of the substrate.

[0016] Another continuous electrocoat apparatus is provided for applyinga coating onto a substantially flat substrate, e.g., anelectroconductive substrate in coil or blank form. The apparatuscomprises a first electrocoat tank having a coating region and anon-conductive conveyor extending at least partially into the firstelectrocoat tank and defining a conveyor path. A plurality ofelectrically conductive supports are carried on the conveyor. Aconnecting system is configured to selectively place at least a portionof the supports in electrical contact with an electrical power sourcewhen the selected supports are in the coating region of the firstelectrocoat tank. A plurality of first electrodes are positioned in thefirst electrocoat tank, with the first electrodes located on a firstside of the conveyor path.

[0017] Another continuous electrocoat apparatus of the inventioncomprises a first electrocoat tank having a coating region with anon-conductive conveyor extending at least partly into the firstelectrocoat tank and defining a conveyor path. The conveyor comprises aplurality of laterally spaced, non-conductive chains movably mounted onrotatable sprockets such that the chains move at substantially the samespeed. A plurality of electrically conductive supports are carried oneach chain to form a support surface of the conveyor. A plurality ofgrounding bars are carried on the conveyor, with each grounding barconnected to at least one support. A bus bar is located adjacent theelectrocoat tank, with the bus bar configured to contact one or moregrounding bars carried on a portion of the conveyor in the coatingregion of the first electrocoat tank.

[0018] A method is provided for applying a coating onto at least aportion of a substantially flat substrate having two major surfaces. Themethod comprises the steps of conveying the substrate between at leastone first electrode and at least one second electrode in a first coatingregion to apply a first aqueous electrodepositable coating compositiononto both major surfaces of the substrate; and conveying the substrateadjacent at least one third electrode located in a second coating regionto apply a second aqueous electrodepositable coating composition ontosubstantially one major surface of the substrate.

[0019] A further method is provided for electrocoating a substantiallysubstrate having two major surfaces. The method comprises the steps ofplacing the substrate onto a non-conductive conveyor having a pluralityof conductive supports defining a support surface, with the conveyordefining a conveyor path through a coating region of an electrocoatbath.

[0020] An electric potential is applied to the substrate when thesubstrate is in the coating region. The substrate is conveyed throughthe coating region adjacent at least one electrode to apply an aqueouselectrodepositable coating composition onto at least one major surfaceof the substrate. The coated substrate is dried and/or cured at a dryingstation located downstream of the electrocoat bath.

DESCRIPTION OF THE INVENTION

[0021] As used herein, spatial or directional terms, such as “left”,“right”, “inner”, “outer”, “above”, “below”, “top”, “bottom”, and thelike, relate to the invention as it is shown in the drawing figures.However, it is to be understood that the invention may assume variousalternative orientations and, accordingly, such terms are not to beconsidered as limiting. Further, as used herein, all numbers expressingdimensions, physical characteristics, processing parameters, quantitiesof ingredients, reaction conditions, and the like used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical values set forth in the following specificationand claims are approximations that may vary depending upon the desiredproperties sought to be obtained by the present invention. At the veryleast, and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical value should atleast be construed in light of the number of reported significant digitsand by applying ordinary rounding techniques. Moreover, all rangesdisclosed herein are to be understood to encompass any and all subrangessubsumed therein. For example, a stated range of “1 to 10” should beconsidered to include any and all subranges between (and inclusive of)the minimum value of 1 and the maximum value of 10; that is, allsubranges beginning with a minimum value of 1 or more and ending with amaximum value of 10 or less, e.g., 5.5 to 10. Molecular weightquantities used herein, whether Mn or Mw, are those determinable fromgel permeation chromatography using polystyrene as a standard. Also, asused herein, the term “polymer” is meant to refer to oligomers,homopolymers, and copolymers. The terms “flat” or “substantially flatsubstrate” refer to a substrate that is substantially planar in form,that is a primarily level substrate lying in a geometric plane, which,as would be understood by one skilled in the art, can include slightbends, projections, or depressions therein.

[0022] The structural components of an exemplary electrocoatingapparatus incorporating features of the invention will first bedescribed and then the use of the electrocoating apparatus to practicean exemplary method of the invention will be described. It is to beunderstood that the specifically disclosed apparatus and method arepresented simply to explain the general concepts of the invention andthat the invention is not limited to these specific embodiments.

[0023] With reference to FIG. 1, an electrocoating apparatus 10 of theinvention includes an electrocoat tank 12 (first electrocoat tank) witha conveyor 14 extending at least partly into the interior of the tank12. The electrocoat tank 12 may be of any conventional type and size toaccommodate the substrates being coated. The dimensions and capacity ofthe tank 12 can vary depending upon the size, e.g., length, width, etc.,of the substrate. In one non-limiting embodiment, the tank 12 has acapacity of 1,000 gallons to 20,000 gallons (3,800 liters to 76,000liters), such as 1,000 gallons to 10,000 gallons (3,800 liters to 38,000liters), e.g., 2,000 gallons to 5,000 gallons (7,600 liters to 19,000liters). In one non-limiting exemplary embodiment, the tank 12 can havea length of 5 feet to 50 feet (1.5 m to 15 m), such as 15 feet to 20feet (4.5 m to 6 m), e.g., 17 feet (5.1 m); a width of 5 feet to 50 feet(1.5 m to 15 m), such as 5 feet to 10 feet (1.5 m to 3 m), e.g., 7 feetto 8 feet (2.1 m to 2.4 m); and a depth of 2 feet to 20 feet (0.6 m to 6m), such as 4 feet to 10 feet (1.2 m to 3 m), e.g., 5 feet to 6 feet(1.5 m to 1.8

[0024] As discussed in more detail below, the tank 12 is configured tocontain an electrodepositable coating composition. The interior of thetank 12 can be in flow communication with a conventional recyclingsystem, e.g., through conduits or pipes, having a pump that recirculatesat least a portion of the coating composition located in the tank 12 toprevent solids in the coating composition from settling to the bottom ofthe tank 12. Additionally, the tank 12 can be in flow communication witha conventional heat exchanger, such as an electric heater, in anyconventional manner, such as through pipes or conduits, to control thetemperature of the coating composition in the tank 12. Further, theinterior of the tank 12 may be in flow communication with a conventionalultrafiltration system to remove soluble impurities from the coatingcomposition and to recycle the filtered material back into theelectrodeposition tank 12.

[0025] In an ultrafiltration system, the coating composition flows overa membrane permeable to water and small particles, e.g., those less than1,000 Mw, such as salts. The ultrafiltrate or “permeate”, i.e., theportion of the coating composition which passes through the membrane,can be used in rinsing operations as described below and a portion ofthe permeate, e.g., 20 weight percent, is typically discarded. The“non-permeate” portion of the coating composition is directed back tothe tank 12, e.g., through one or more conduits or pipes. The structureand operation of conventional recycling, heat exchanger, andultrafiltration systems will be well understood by one of ordinary skillin the art and, hence, such systems will not be described in detailherein. Examples of such conventional systems and conventionalelectrocoat tanks are disclosed, for example but not to be considered aslimiting, in U.S. Pat. Nos. 4,333,807 and 4,259,163, herein incorporatedby reference.

[0026] As shown on the left side of FIG. 1, a load area 16 is definedadjacent one end of the conveyor 14. The load area 16 can be defined,for example, by an area 5 feet to 10 feet (1.5 m to 3 m) long extendingthe width of the tank 12 and having sufficient free space to permitunhindered loading of substrates to be coated, whether in blank or coilform, onto the conveyor 14 as described in more detail below.

[0027] The conveyor 14 of the invention has an inlet end 18 and anoutlet end 20. For coating blanks, the conveyor 14 may be of anyconvenient type, such as, but not limited to, a belt conveyor, a chainconveyor, a platform conveyor, and the like. However, the conveyor 14 istypically composed primarily of non-conductive material so as not toattract electrodepositable coating material during the coating process.In the exemplary embodiment of the apparatus 10 shown in FIGS. 1-3, theconveyor 14 is an endless or “closed-loop” conveyor formed from aplurality of mutually spaced, movable and deformable or flexible membersdefining an outer conveyor surface facing away from the apparatus 10 andan inner conveyor surface facing the interior of the apparatus 10. Aswill be appreciated by one of ordinary skill in the art, the exemplaryendless conveyor 14 shown in FIG. 1 provides an upper portion or leg totransport substrates during the coating process and a lower or returnportion. Examples of materials suitable for the flexible members includepolymeric material, e.g., plastic material, or non-conductive metals,such as aluminum or poly-steel chains such as those commerciallyavailable from Tsubaki Corp. of Japan. For example, as shown in FIGS. 1and 2, the conveyor 14 may be formed by a plurality, e.g., 5, spaced,non-conductive chains 22 each movably mounted on rotatable wheels,rollers, or sprockets 24 and supported on guide devices, such as guiderails, to define a conveyor path P into and out of the electrocoat tank12. In the exemplary embodiment shown in FIGS. 1-3, the non-conductivechains 22 are laterally spaced 1″ to 24″ (2.5 cm to 61 cm) apart,typically 5″ to 11″ (13 cm to 28 cm) apart.

[0028] In order to help maintain a substrate on the conveyor 14 duringthe coating process, a plurality of holding devices can be carried onthe conveyor 14. For example, as shown in FIG. 3 a plurality of magnets25 can be carried on or attached to or between the chains 22. In oneembodiment of the present invention, the magnets 25 are located at ornear the inner surface of the conveyor 14 and do not extend above thetop or outer surface of the conveyor 14 such that the magnets do notcontact a substrate located on the conveyor 14. Alternatively, themagnets 25 can be located on the guide rails over which the conveyor 14travels.

[0029] In order to electrocoat a substrate, the substrate should beunder the influence of an applied electric potential. Therefore, aconnecting system 26 is provided to connect the substrate to be coatedto an electrical source (not shown) during the coating process. In theexemplary embodiment shown in FIGS. 1-3, the connecting system 26includes a plurality of spaced, electrically conductive supports 28(FIG. 3) carried on the chains 22 and extending above the top or outersurface of the conveyor 14 to support and contact a metal substrateduring the coating process as described below. For example, the supports28 can be carried on or attached to each chain 22 at evenly spacedintervals, e.g., 6 inch to 12 inch (15 cm to 31 cm) intervals, on thechain 22. The supports 28 on adjacent chains 22 can be aligned to formspaced rows of supports 28 extending across the width of the conveyor14. A timing shaft (not shown) can be attached to the sprockets 24 sothat the chains 22 move at substantially the same speed to maintain thesupports 28 in rows. Examples of suitable supports 28 for the practiceof the invention include K-1 electrical connectors commerciallyavailable from 3I Engineering of Evansville, Ind. Of course, theinvention is not limited to forming such rows of supports 28. Thesupports 28 on adjacent chains 22 can be offset from one another, ifdesired.

[0030] In order to provide the electric potential, the supports 28 canbe connected to one or more electrically conductive connectors. Forexample, the connectors can be solid, metal, electrically conductivegrounding bars 30 (FIGS. 2 and 3), each connected to one or more of thesupports 28. The grounding bars 30 can be carried on the chains 22 tomove when the chains 22 move. For example, one grounding bar 30 can beconnected to each of the adjacent supports 28 of a row as describedabove. Each grounding bar 30 may have an outer end 32, e.g., extendingabove the outer surface of the conveyor 14. So as not to clutter thefigures, only a portion of the total number of grounding bars 30 areshown in FIG. 1. The outer ends 32 of the grounding bars 30 define apath 34 shown in dashed lines in FIG. 1 as the conveyor 14 moves. Asdescribed below, the grounding bars 30 act to place one or more selectedsupports 28 in electrical contact with the electrical power source toapply an electric potential to a substrate carried on the selectedsupports 28 when the selected supports 28 supporting the substrate areadjacent to or in the tank 12, particularly in a coating region of thetank 12, as described in more detail below.

[0031] The grounding bars 30, e.g., the outer ends 32 of the groundingbars 30, are configured to contact an electrical bus bar 36 mountedadjacent, e.g., above, the electrocoat tank 12. As shown in FIG. 1, thebus bar 36 is shaped, e.g., curved, such that, as described in moredetail below, the outer end 32 of a grounding bar 30 contacts the busbar 36 when the supports 28 to which the grounding bar 30 is connectedare positioned in or adjacent the electrocoating composition in the tank12 but loses contact with the bus bar 30 when the supports 28 connectedto the grounding bar 30 pass out of the electrocoating composition orout of the coating region of the tank 12.

[0032] As will be appreciated by one of ordinary skill in the art, theinvention is not limited to connecting systems having the grounding barand bus bar structure described above. For example, the connectingsystem 26 could be formed by a plurality of electrically conductivedriven contact wheels forming part of the conveyor or by opposed contactclamps configured to engage the substrate when located in the tank 12.Non-limiting examples of suitable alternative connecting systems aredisclosed in U.S. Pat. Nos. 4,385,967 and 4,755,271, herein incorporatedby reference.

[0033] At least one and typically a plurality of first electrodes 40 arelocated in the electrocoat tank 12 on one side of the conveyor path,e.g., above the conveyor path as shown in FIG. 1. The first electrodes40 can be located less than 10″ (25 cm) from the top of the conveyor 14,i.e., the side of the upper leg of the conveyor 14 closest the firstelectrodes 40, are often less than 5″ (12.5 cm) from the top of theconveyor 14, and usually are less than 1″ to 2″ (2.5 cm to 5 cm) fromthe top of the conveyor 14. The first electrodes 40 can be attached toor carried on a vertically movable support (not shown) such that thedistance between one or more of the first electrodes 40 and the top ofthe conveyor 14 can be adjusted. The first electrodes 40 are disposed inthe tank 12 transverse to the conveyor path. The electrodes 40 areconnected to a power source (not shown) in any suitable manner, such asby cables. The electrodes 40 are made of electrically conductivematerial, such as copper, and may be configured as copper bars extendingacross the width of the conveyor 14 in the tank 12.

[0034] As described more fully below, one or more optional secondelectrodes 42 can be located in the electrocoat tank 12 below the upperleg of the conveyor path P, e.g., opposite the first electrodes 40. Ifpresent, the second electrodes 42 are typically located 1″ to 10″ (2.5cm to 25 cm) from the bottom of the upper leg of the conveyor 14. Thesecond electrodes 42 also can be attached to or carried on one or moremovable supports such that the distance between one or more of thesecond electrodes 42 and the bottom of the upper conveyor 14 portion canbe adjusted.

[0035] An exit rinse station 44 can be located at or near a dischargeend of the tank 12. The rinse station 44 can comprise one or more sprayapplicators 45 in flow communication with a source of rinsing fluid,e.g., one or more applicators located above the conveyor path P of theupper portion of the conveyor 14 and one or more applicators 45 belowthe upper portion of the conveyor 14. For example, the spray applicators45 can be in flow communication with the ultrafiltration system toprovide permeate to the rinse applicators 45. Excess rinse fluid can bedirected into the tank 12, e.g., by a sloped shelf located under therinse applicators 45 and sloping toward the tank 12.

[0036] A first rinse station 46 is located downstream (with respect to adirection of movement of the conveyor) of the electrocoat tank 12, e.g.,downstream of the exit rinse station 44. The first rinse station 46 cancomprise any conventional rinse applicators but, in the exemplaryembodiment under discussion, includes one or more spray applicators 48located above and in flow communication with a first rinse tank 50,e.g., by a pump and conduits to supply rinse fluid from the first rinsetank 50 to the spray applicators 48. The first rinse tank 50 may also bein flow communication with a conventional recirculation system having arecirculation pump (not shown). As shown in FIG. 1, one or more of theapplicators 48 can be located above the upper portion of the conveyor 14(and directed toward the outer surface of the conveyor 14) and one ormore other of the applicators 48 can be located below the upper portionof the conveyor 14 (and directed toward the inner surface of theconveyor 14).

[0037] A first drain station 52 is located downstream of the first rinsestation 46 to remove at least some of the excess rinse composition fromthe surfaces of the substrate being coated. The first drain station 52can include one or more fluid removal devices, such as an air knife orsqueegee rolls. In the exemplary embodiment shown in FIG. 1, the firstdrain station 52 includes two air knives 54, with one air knife 54located above the conveyor path and another air knife 54 located belowthe conveyor path. The air knives 54 are configured to direct or blow atleast some of the excess rinse composition back into the first rinsetank 46.

[0038] A second rinse station 58 is located downstream of the firstrinse station 46. The second rinse station 58 can comprise anyconventional rinsing applicators but, in the exemplary embodiment underdiscussion, includes one or more spray applicators 60 located above andin flow communication with a second rinse tank 64, e.g., by a pump andconduits to supply rinse fluid from the second rinse tank 64 to thespray applicators 60 in similar manner as in the first rinse station 46.The second rinse tank 64 may be in flow communication with aconventional recirculation system having a recirculation pump (notshown).

[0039] A second drain station 68 is located downstream of the secondrinse station 58 to remove at least some of the excess rinse compositionfrom the substrate. The second drain station 68 includes at least onefluid removal device, such as one air knife 70 located above theconveyor path and another air knife 70 located below the conveyor path.The air knives 70 are configured to direct at least some of the excessrinse composition back into the second rinse tank 64.

[0040] A drying station 74 having a dryer 76 is located downstream ofthe second rinse tank 64 to dry and/or cure the applied coating. As usedherein, the term “dry” means the almost complete absence of water fromthe coating and the term “cure” means that the majority, preferably all,of any crosslinkable components of the applied coating material arecrosslinked. The dryer 76 can include any conventional drying oven ordrying apparatus, such as an infra-red radiation oven, an electric oven,a gas oven, a hot air convection oven, and the like. In one exemplaryembodiment, the dryer 76 is a high velocity gas oven commerciallyavailable from Gruenwald Corp. of Germany.

[0041] A dryer conveyor 78 extends between the discharge end of theconveyor 14 and the entrance to the dryer 76. The dryer conveyor 78 canbe of any conventional type, such as a belt conveyor, roller conveyor,skate-wheel conveyor, and the like.

[0042] An optional induction heater 80 can be located around at least aportion of the dryer conveyor 78 prior to the entrance to the dryer 76.The induction heater 80 preferably surrounds the dryer conveyor 78 andinduces a field that induces a current that generates heat.

[0043] Having described the structural components of an exemplaryelectrocoat apparatus 10, an exemplary method of priming and topcoatinga substrate by a continuous electrocoating process utilizing one or moreapparatus 10 in accordance with the invention will now be described. By“continuous electrocoating process” is meant that the substrate is incontinuous movement throughout the coating process. Although the processcan be practiced on substrates in blank or coil form, the followingexemplary method will first be discussed with reference toelectrocoating blanks with a primer coating on both major surfaces andthen a subsequent electrodeposited topcoat primarily on one majorsurface.

[0044] The substrates used in the practice of the present inventiontypically are metallic substrates and can include ferrous metals andnon-ferrous metals. Suitable ferrous metals include iron, steel, andalloys thereof. Non-limiting examples of useful steel materials includecold-rolled steel, galvanized (zinc coated) steel, electrogalvanizedsteel, stainless steel, pickled steel, GALVANNEAL®, GALVALUME®, andGALVAN® zinc-aluminum alloys coated upon steel, and combinationsthereof. Useful non-ferrous metals include aluminum, zinc, magnesium andalloys thereof. Combinations or composites of ferrous and non-ferrousmetals can also be used.

[0045] As shown in FIG. 4, the metal substrate can be cut or punched toform a flat metal blank of a desired configuration and/or cleaned,degreased, and/or a corrosion resistant coating applied at one or morepretreatment stations 82. Before depositing coatings upon the surface ofthe metallic substrate, it is preferred to remove foreign matter fromthe metal surface by thoroughly cleaning and/or degreasing the substratesurface. As used herein, the terms “deposited upon”, “applied onto”, and“provided upon” a substrate mean deposited or provided above or over butnot necessarily adjacent to the surface of the substrate. For example, acoating “deposited upon” a substrate can be deposited directly on thesubstrate or one or more other coatings can be located therebetween.

[0046] The surface of the metallic substrate can be cleaned by physicalor chemical means, such as mechanically abrading the surface or, as ispreferred, cleaning/degreasing with commercially available alkaline oracidic cleaning agents which are well known to those skilled in the art,such as sodium metasilicate and sodium hydroxide. Non-limiting examplesof preferred cleaning agents include CHEMKLEEN® 163 and CHEMKLEEN® 177phosphate cleaners, both of which are commercially available from PPGIndustries, Inc. of Pittsburgh, Pennsylvania.

[0047] Following the cleaning step, the surface of the metallicsubstrate may be rinsed with water, typically deionized water, in orderto remove any residue. Optionally, the metal surface can be rinsed withan aqueous acidic solution after cleaning with the alkaline cleaners.Examples of rinse solutions include mild or strong acidic cleaners suchas the dilute nitric acid solutions commercially available andconventionally used in metal pretreatment processes. The metallicsubstrate can be air-dried using an air knife, by flashing off the waterby brief exposure of the substrate to a high temperature, or by passingthe substrate between squeegee rolls.

[0048] Optionally, a phosphate-based pretreatment or conversion coatingcan be applied to the metallic substrate. Suitable phosphate conversioncoating compositions include those known in the art, such as zincphosphate, optionally modified with nickel, iron, manganese, calcium,magnesium or cobalt. Useful phosphating compositions are described inU.S. Pat. Nos. 4,793,867 and 5,588,989; 4,941,930; 5,238,506 and5,653,790.

[0049] With reference to FIGS. 1 and 4, pretreated metal blanks 84 areloaded onto the inlet end 18 of the conveyor 14 at the load area 16. Theblanks 84 can be supplied to the load area 16 in any desired manner,such as by a conveyor, a fork lift truck, on pallets, by overhead crane,etc., and then placed on the conveyor 14 by a worker or directly by thesupply device. Because the supports 28 protrude above the top of theconveyor 14, e.g., above the outer or top surface of the chains 22, theblank 84 is supported totally on the supports 28 and does not contactthe chains 22 themselves. The top portion of the supports 28 are taperedor pointed to minimize the area of contact between the bottom of theblank 84 and the top of the supports 28 on which it rests. The supports28 should be sufficiently tapered or pointed to minimize the contactarea with the bottom of the blank 84 but should not be so pointed thatthe points damage the bottom surface of the blank 84 or damage anyprevious coatings which may have been applied to the blank 84.

[0050] In the exemplary embodiment of FIGS. 1 and 4, the conveyor 14conveys the blank 84 to the right toward the tank 12. As the blank 84 ismoved from the load area 16 toward the electrocoat tank 12, the supports28 on which the blank rests are typically not in contact with a sourceof electrical potential. In the exemplary embodiment under discussion,this is because the outer ends 32 of the grounding bars 30 connected tothe supports 28 on which the blank 84 rests are not in contact with thebus bar 36. When the conveyor 14, and hence the blank 84, begins todescend into the electrocoat composition in the tank 12 (into the firstcoating region), the forward most (right most) grounding bar 30connected to the forward most (right most) supports 28 carrying theblank 84 contacts the left end of the bus bar 36 to electrically groundthe forward most supports 28, and hence the blank 84 resting thereon, tothe bus bar 30. Electrical current is conducted through the groundingbar 30 and the supports 28 to the blank 84 to apply an electricalpotential to the blank 84. As shown in FIGS. 2 and 3, the outer end 32of the grounding bar 30 can be bent or have an “L-shaped” contact region86 which contacts and slides along the bus bar 36 to maintain theelectrical connection as the conveyor 14 continues to move. As theconveyor 14 moves to the right in FIG. 1, the subsequent grounding bars30 connected to the supports 28 on which the blank 84 rests sequentiallycome into contact with the bus bar 36 in similar manner as describedabove to apply an electric potential to the supports 28 connectedthereto and, hence, to the blank 84 carried thereon. In theelectrocoating process of the invention, the blank 84 serves as anelectrode, e.g., a cathode, in an electrical circuit comprising theblank (electrode) and the electrodes 40 and/or 42 (counter-electrodes)immersed in the coating composition as described below.

[0051] Assuming a coating, e.g., a primer coating, is to be applied toboth major surfaces of the blank 84, both the first and secondelectrodes 40, 42 are energized during the coating process. Theelectrodes 40, 42 are preferably positioned to be less than 1″ to 5″(2.5 cm to 12.5 cm) from the respective top and bottom major surfaces ofthe blank 84, such as less than 1″ (2.5 cm) during the coating process.As the conveyor 14 moves the charged blank 84 between the electrodes 40,42 in the first coating region, the electrodepositable coatingcomposition in the tank 14 is deposited over both major surfaces and theedges of the blank 84.

[0052] As will be appreciated by one of ordinary skill in the art, inthe process of applying the first electrodepositable coating, theaqueous dispersion of the electrodepositable composition is placed incontact with an electrically conductive anode and cathode. Upon passageof an electric current between the anode and cathode, an adherent filmof the electrodepositable composition will deposit in a substantiallycontinuous manner on the substrate serving as either the anode or thecathode depending on whether the composition is anionically orcationically electrodepositable. Electrodeposition is usually carriedout at a constant voltage ranging from 1 volt to 7,000 volts, andtypically between 50 and 500 volts. Current density is usually between1.0 ampere and 15 amperes per square foot (10.8 to 161.5 amperes persquare meter).

[0053] As will be appreciated by one of skill in the art, the amount ofthe coating composition applied to the blank 84 depends on severalfactors, such as the throwpower of the coating composition, thetemperature of the coating composition, the voltage applied to theelectrodes, and the dwell time of the blank in the coating composition.As used herein, the term “dwell time” refers to the length of time thecharged substrate is positioned in the tank 12 adjacent one or more ofthe electrodes 40 and/or 42 (i.e. in the coating region). In oneexemplary embodiment, the coating composition can have a temperature of70° F. to 100° F. (21° C. to 38° C.), e.g., 80° F. to 90° F. (27° C. to32° C.), an applied voltage of 1V to 450V, such as 1V to 300V, and aconveyor speed sufficient to provide a dwell time of 10 secs to 30 secs,e.g., 15 secs. In one exemplary embodiment, the apparatus 10 isconfigured such that a conveyor speed of 20 feet per minute (FPM) (6meters per minute (MPM)) provides a dwell time of 15 secs. Assuming theapplied coating is a primer coating, the deposition conditions are setto provide a dried primer coating thickness of 0.15 mil to 0.25 mil(0.004 mm to 0.006 mm) on both major surfaces of the blank 84. Inanother exemplary embodiment, the conveyor speed can be in the range of50 ft/min to 1000 ft/min (15 meters/min to 305 meters/min).

[0054] An exemplary electrodeposition bath composition useful in thepractice of the present invention comprises a resinous phase dispersedin an aqueous medium. The resinous phase includes a film-forming organiccomponent which can comprise an anionic electrodepositable coatingcomposition, or, as is preferred, a cationic electrodepositable coatingcomposition. The electrodepositable coating composition typicallycomprises an active hydrogen group-containing ionic resin and a curingagent having functional groups reactive with the active hydrogens of theionic resin. As used herein, the term “reactive” refers to a functionalgroup that forms a covalent bond with another functional group undersuitable reaction conditions.

[0055] Non-limiting examples of anionic electrodepositable coatingcompositions include those comprising an ungelled, water-dispersibleelectrodepositable anionic film-forming resin. Examples of film-formingresins suitable for use in anionic electrodeposition coatingcompositions are base-solubilized, carboxylic acid containing polymers,such as the reaction product or adduct of a drying oil or semi-dryingfatty acid ester with a dicarboxylic acid or anhydride; and

[0056] the reaction product of a fatty acid ester, unsaturated acid oranhydride and any additional unsaturated modifying materials which arefurther reacted with polyol. Also suitable are the at least partiallyneutralized interpolymers of hydroxy-alkyl esters of unsaturatedcarboxylic acids, unsaturated carboxylic acid and at least one otherethylenically unsaturated monomer. Yet another suitableelectrodepositable anionic resin comprises an alkyd-aminoplast vehicle,i.e., a vehicle containing an alkyd resin and an amine-aldehyde resin.Yet another anionic electrodepositable resin composition comprises mixedesters of a resinous polyol.

[0057] These compositions are described in detail in U.S. Pat. No.3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to 13. Otheracid functional polymers can also be used such as phosphatizedpolyepoxide or phosphatized acrylic polymers as are well known to thoseskilled in the art.

[0058] By “ungelled” is meant that the polymer is substantially free ofcrosslinking and has an intrinsic viscosity when dissolved in a suitablesolvent. The intrinsic viscosity of a polymer is an indication of itsmolecular weight. A gelled polymer, on the other hand, since it is ofessentially infinitely high molecular weight, will have an intrinsicviscosity too high to measure.

[0059] With reference to the cationic resin, a wide variety of cationicpolymers are known and can be used in the compositions of the inventionso long as the polymers are “water dispersible,” i.e., adapted to besolubilized, dispersed or emulsified in water. The water dispersibleresin is cationic in nature, that is, the polymer contains cationicfunctional groups to impart a positive charge. The cationic resin mayalso contain active hydrogen groups.

[0060] Examples of cationic resins suitable include onium saltgroup-containing resins such as ternary sulfonium salt group-containingresins and quaternary phosphonium salt-group containing resins, forexample, those described in U.S. Pat. Nos. 3,793,278 and 3,984,922,respectively. Other suitable onium salt group-containing resins includequaternary ammonium salt group-containing resins, for example, thosewhich are formed from reacting an organic polyepoxide with a tertiaryamine salt. Such resins are described in U.S. Pat. Nos. 3,962,165;3,975,346; and 4,001,101. Also suitable are the amine saltgroup-containing resins such as the acid-solubilized reaction productsof polyepoxides and primary or secondary amines such as those describedin U.S. Pat. Nos. 3,663,389; 3,984,299; 3,947,338 and 3,947,339.

[0061] Usually, the above-described salt group-containing resinsdescribed above are used in combination with a blocked isocyanate curingagent. The isocyanate can be fully blocked as described in theaforementioned U.S. Pat. No. 3,984,299 or the isocyanate can bepartially blocked and reacted with the resin backbone such as isdescribed in U.S. Pat. No. 3,947,338.

[0062] Also, one-component compositions as described in U.S. Pat. No.4,134,866 and DE-OS No. 2,707,405 can be used as the cationic resin.Besides the epoxy-amine reaction products, resins can also be selectedfrom cationic acrylic resins such as those described in U.S. Pat. Nos.3,455,806 and 3,928,157. Also, cationic resins which cure viatransesterification such as described in European Application No. 12463can be used. Further, cationic compositions prepared from Mannich basessuch as described in U.S. Pat. No. 4,134,932 can be used. Also useful inthe electrodepositable coating compositions of the present invention arethose positively charged resins which contain primary and/or secondaryamine groups. Such resins are described in U.S. Pat. Nos. 3,663,389;3,947,339; and 4,115,900. U.S. Pat. No. 3,947,339 describes apolyketimine derivative of a polyamine such as diethylenetriamine ortriethylenetetraamine with the excess polyamine vacuum stripped from thereaction mixture. Such products are described in U.S. Pat. Nos.3,663,389 and 4,116,900.

[0063] In one embodiment of the present invention, the cationic resinssuitable for inclusion in the electrodepositable coating compositionsuseful in the methods of the present invention are onium saltgroup-containing acrylic resins.

[0064] The cationic resin described immediately above is typicallypresent in the electrodepositable coating compositions in amounts of 1to 60 weight percent, such as 5 to 25 weight percent based on totalweight of the composition.

[0065] As previously discussed, the electrodepositable coatingcompositions which are useful in the methods of the present inventiontypically further comprise a curing agent which contains functionalgroups which are reactive with the active hydrogen groups of the ionicresin.

[0066] Aminoplast resins, which are the preferred curing agents foranionic electrodeposition, are the condensation products of amines oramides with aldehydes. Examples of suitable amine or amides aremelamine, benzoguanamine, urea and similar compounds. Generally, thealdehyde employed is formaldehyde, although products can be made fromother aldehydes such as acetaldehyde and furfural. The condensationproducts contain methylol groups or similar alkylol groups depending onthe particular aldehyde employed. These methylol groups can beetherified by reaction with an alcohol. Various alcohols employedinclude monohydric alcohols containing from 1 to 4 carbon atoms such asmethanol, ethanol, isopropanol, and n-butanol, with methanol beingpreferred. Aminoplast resins are commercially available from AmericanCyanamid Co. under the trademark CYMEL® and from Monsanto Chemical Co.under the trademark RESIMENE®.

[0067] The aminoplast curing agents are typically utilized inconjunction with the active hydrogen containing anionicelectrodepositable resin in amounts ranging from 5 percent to 60 percentby weight, such as from 20 percent to 40 percent by weight, thepercentages based on the total weight of the resin solids in theelectrodeposition bath.

[0068] The preferred curing agents for cationic electrodepositablecoating compositions are blocked organic polyisocyanates. Thepolyisocyanates can be fully blocked as described in U.S. Pat. No.3,984,299 column 1 lines 1 to 68, column 2 and column 3 lines 1 to 15,or partially blocked and reacted with the polymer backbone as describedin U.S. Patent No. 3,947,338 column 2 lines 65 to 68, column 3 andcolumn 4 lines 1 to 30. By “blocked” is meant that the isocyanate groupshave been reacted with a compound so that the resultant blockedisocyanate group is stable to active hydrogens at ambient temperaturebut reactive with active hydrogens in the film forming polymer atelevated temperatures, usually between 90° C. and 200° C.

[0069] Suitable polyisocyanates include aromatic and aliphaticpolyisocyanates, including cycloaliphatic polyisocyanates andrepresentative examples include diphenylmethane-4,4′-diisocyanate (MDI),2,4- or 2,6-toluene diisocyanate (TDI), including mixtures thereof,p-phenylene diisocyanate, tetramethylene and hexamethylenediisocyanates, dicyclohexylmethane-4,4-diisocyanate, isophoronediisocyanate, mixtures of phenylmethane-4,4′-diisocyanate andpolymethylene polyphenylisocyanate. Higher polyisocyanates such astriisocyanates can be used. An example would includetriphenylmethane-4,4′,4″ -triisocyanate. Isocyanate prepolymers withpolyols such as neopentyl glycol and trimethylolpropane and withpolymeric polyols such as polycaprolactone diols and triols (NCO/OHequivalent ratio greater than 1) can also be used.

[0070] The polyisocyanate curing agents are typically utilized inconjunction with the cationic resin in amounts ranging from 1 weightpercent to 65 weight percent, such as from 5 weight percent to 45 weightpercent, based on the weight of the total resin solids presentcomposition.

[0071] The aqueous compositions of the present invention are in the formof an aqueous dispersion. The term “dispersion” is believed to be atwo-phase transparent, translucent or opaque resinous system in whichthe resin is in the dispersed phase and the water is in the continuousphase.

[0072] The average particle size of the resinous phase is generally lessthan 1.0 and usually less than 0.5 microns, such as less than 0.15micron.

[0073] The concentration of the resinous phase in the aqueous medium isat least 1 and usually from 2 to 60 percent by weight based on totalweight of the aqueous dispersion. When the compositions of the presentinvention are in the form of resin concentrates, they generally have aresin solids content of 20 to 60 percent by weight based on weight ofthe aqueous dispersion.

[0074] Electrodeposition compositions useful in the methods of thepresent invention are typically supplied as two components: (1) a clearresin feed, which includes generally the active hydrogen-containingionic electrodepositable resin, i.e., the main film-forming polymer, thecuring agent, and any additional water-dispersible, non-pigmentedcomponents; and (2) a pigment paste, which generally includes one ormore pigments, a water-dispersible grind resin which can be the same ordifferent from the main-film forming polymer, and, optionally, additivessuch as wetting or dispersing aids. Electrodeposition bath components(1) and (2) are dispersed in an aqueous medium which comprises waterand, usually, coalescing solvents.

[0075] The electrodeposition composition of the present invention has aresin solids content usually within the range of 5 to 25 percent byweight based on total weight of the electrodeposition composition.

[0076] As aforementioned, besides water, the aqueous medium may containa coalescing solvent. Useful coalescing solvents include hydrocarbons,alcohols, esters, ethers and ketones.

[0077] The preferred coalescing solvents include alcohols, polyols andketones. Specific coalescing solvents include isopropanol, butanol,2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and propyleneglycol and the monoethyl, monobutyl and monohexyl ethers of ethyleneglycol. The amount of coalescing solvent is generally between 0.01 and25 percent and when used, such as from 0.05 to 5 percent by weight basedon total weight of the aqueous medium.

[0078] As discussed above, a pigment composition and, if desired,various additives such as surfactants, wetting agents or catalyst can beincluded in the dispersion. The pigment composition may be of theconventional type comprising pigments, for example, iron oxides,strontium chromate, carbon black, coal dust, titanium dioxide, talc,barium sulfate, as well as color pigments such as cadmium yellow,cadmium red, chromium yellow and the like.

[0079] The pigment content of the dispersion is usually expressed as apigment-to-resin ratio. In the practice of the invention, when pigmentis employed, the pigment-to-resin ratio is usually within the range of0.02 to 1:1. The other additives mentioned above are usually in thedispersion in amounts of 0.01 to 3 percent by weight based on weight ofresin solids.

[0080] As will be understood from FIGS. 1-3, as the blank 84 movesthrough the electrocoat tank 12 on the conveyor 14, the supports 28supporting the blank 84 are in contact with the bus bar 38 through thegrounding bar 30 when the blank 84 is between and/or adjacent theelectrodes 40 and/or 42 (i.e. in the first coating region), thussupplying electrical current to the blank 84 during the coating process.As the conveyor 14 continues to move to the right, the grounding bars 30connected to the supports 28 supporting the right end (forward end) ofthe blank 84 slide off of and no longer contact the bus bar 38, thus noelectrical power is supplied to those supports 28. As the blank 84continues to move to the right on the conveyor 14, the remaininggrounding bars 30 connected to the supports 28 carrying the blank 84continue to lose contact with the bus bar 36 until eventually all of thesupports 28 supporting the blank 84 are no longer in contact with thebus bar 38 and the blank 84 emerges from the electrocoating composition.

[0081] Upon emergence, the coated blank 84 may undergo a surface rinse,e.g., with water or permeate at the exit rinse station 46, to rinsenon-adhered electrocoat material back into the electrocoat tank 12.

[0082] As the conveyor 14 continues to move to the right, the blank 84is conveyed into the first rinse station 46 where an aqueous rinsecomposition is sprayed onto the coated blank 84 by the spray applicators48. Excess rinse composition, e.g., water or permeate, drains back intothe first rinse tank 50 located below the applicators 48 to berecirculated for further rinsing operations. In a currently preferredembodiment, the apparatus 10 is configured such that at a conveyor speedof 20 feet per minute (FPM) (6 meters per minute (MPM)) the blank 84 isin the first rinse station 46 for 5 sec to 20 sec, such as 10 sec to 15sec, e.g., 12 sec.

[0083] As the conveyor 14 moves to the right, the blank 84 istransported into the first drain station 52 between the first set of airknives 54 to help remove excess rinse composition. The air knives 54direct air toward the blank 84. The air knives 54 are positioned to blowexcess rinse composition back into the first rinse tank 50.

[0084] The blank 84 is then moved through the second rinse station 58and the second drain station 68 where the coated blank 84 is rinsed anddrained in similar manner as described above.

[0085] As the conveyor 14 continues to move to the right, the blank 84is transferred from the conveyor 14 at the outlet end 18 onto the dryerconveyor 78 for transport into the dryer 76 to dry and/or cure theelectrodeposited coating as the blank 84 passes through the dryer 76. Inone embodiment of the present invention, after the coating has beenapplied by electrodeposition, it is cured, usually by baking, atelevated temperatures ranging from 90° C. to 430° C. for a periodranging from 60 to 1200 seconds. The dryer can be any of a variety ofcuring ovens, both electric and gas powered, that are well known in theart for use on coating lines. Alternatively, the coating can be curedusing infrared curing techniques as are well known in the art, typicallyfor a period ranging from 45 to 240 seconds or a time sufficient toobtain a peak metal temperature ranging from 300° to 700° F. (148.9° to371.1° C.). In a preferred embodiment of the present invention, thedryer 76 has a temperature of 150° F. to 800° F. (82° C. to 426° C.),e.g., 600° F. to 750° F. (315° C. to 398° C.), such as 650° F. (343°C.), and the dryer conveyor 78 has a speed such that the blank 84 islocated in the dryer 76 for 20 sec to 60 sec, such as 40 sec to 50 sec,e.g., 45 sec. In one embodiment, the electrodeposited coating is driedby driving substantially all the solvent and/or water from the coatingeither by evaporation at ambient temperature or by forced drying atelevated temperatures.

[0086] For curable coating compositions, the coating on the blank 84 iscured or at least partially cured in the dryer 76. In certainembodiments of the present invention, the crosslink density of thecrosslinkable components, i.e., the degree of crosslinking, ranges from5% to 100% of complete crosslinking. In other embodiments, the crosslinkdensity ranges from 35% to 85% of full crosslinking. In otherembodiments, the crosslink density ranges from 50% to 85% of fullcrosslinking. One skilled in the art will understand that the presenceand degree of crosslinking, i.e., the crosslink density, can bedetermined by a variety of methods, such as dynamic mechanical thermalanalysis (DMTA) using a Polymer Laboratories MK III DMTA analyzerconducted under nitrogen. This method determines the glass transitiontemperature and crosslink density of free films of coatings or polymers.These physical properties of a cured material are related to thestructure of the crosslinked network.

[0087] According to this method, the length, width, and thickness of asample to be analyzed are first measured, the sample is tightly mountedto the Polymer Laboratories MK III apparatus, and the dimensionalmeasurements are entered into the apparatus. A thermal scan is run at aheating rate of 3° C./min, a frequency of 1 Hz, a strain of 120%, and astatic force of 0.01N, and sample measurements occur every two seconds.The mode of deformation, glass transition temperature, and crosslinkdensity of the sample can be determined according to this method. Highercrosslink density values indicate a higher degree of crosslinking in thecoating.

[0088] In the method described immediately above, the electrodepositioncomposition in the tank 12 of the apparatus 10 (i.e., the primercomposition) comprises an electrodepositable coating composition whichforms an electroconductive coating on both major surfaces and thesheared edges of the blank 84. This electrodepositable coatingcomposition can be an anionic composition or, as is preferred, acationic composition. The electrodepositable coating composition fromwhich the electroconductive coating is electrodeposited onto bothsurfaces of the blank 84 can be a substantially unpigmented coatingcomposition (i.e., a clearcoat composition) or a pigmented coatingcomposition.

[0089] Generally, the electrodepositable coating compositions which areuseful in the methods of the present invention are applied underconditions such that a substantially continuous coating having a driedfilm-thickness ranging from 0.1 to 1.8 mils (2.54 to 45.72 micrometers),usually from 0.15 to 1.6 mils (30.48 to 40.64 micrometers) is formedupon both major surfaces of the metal blank.

[0090] It should be understood that the coating applied by the methoddescribed immediately above can be an electrocoating primer suitable asa primary coating for subsequent application of a non-electrophoreticcoating.

[0091] Alternatively, the electrocoating can be an appearance-enhancingelectrodeposited top coating. In the case of a primer coating, theelectrodepositable coating composition is such that a substantiallycontinuous primer coating having a dried film-thickness ranging from 0.1to 0.4 mils (2.54 to 81.28 micrometers), usually from 0.15 to 2.5 mils(30.48 to 50.8 micrometers) is formed upon both major surfaces of themetal blank. In the case of an appearance-enhancing top coat, theelectrodepositable coating composition is applied such that asubstantially continuous top coating having a dried film-thicknessranging from 0.8 to 1.8 mils (20.32 to 45.72 micrometers), usually from1.0 to 1.6 mils (25.4 to 40.6 micrometers) is formed upon both majorsurfaces of the metal blank.

[0092] In one embodiment, the electrodepositable coating compositionfrom which the electroconductive coating is deposited onto both surfacesof the blank 84 comprises (a) an electrodepositable ionic resin, and (b)one or more electrically conductive pigments. Non-limiting examples ofelectrodepositable ionic resins suitable for use in theelectrodepositable coating composition include the anionic and cationicfilm-forming polymers described in detail above, as well as thecorresponding curing agents for such ionic polymers.

[0093] The electrodepositable compositions can further comprise one ormore electroconductive pigments to render the resultant coatingelectroconductive. Suitable electroconductive pigments includeelectrically conductive carbon black pigments. Generally the carbonblacks can be any one or a blend of carbon blacks ranging from thosethat are known as higher conductive carbon blacks, i.e. those with a BETsurface area greater than 500 m²/gram and DBP adsorption number(determined in accordance with ASTM D2414-93) of 200 to 600 ml/100 g. tothose with lower DBP numbers on the order of 30 to 120 ml/100 gram suchas those with DBP numbers of 40 to 80 ml/100 grams.

[0094] Examples of commercially available carbon blacks include CabotMonarch™ 1300, Cabot XC-72R, Black Pearls 2000 and Vulcan XC 72 sold byCabot Corporation; Acheson Electrodag™ 230 sold by Acheson Colloids Co.;Columbian Raven™ 3500 sold by Columbian Carbon Co.; and Printex™ XE 2,Printex 200, Printex L and Printex L6 sold by DeGussa Corporation,Pigments Group. Suitable carbon blacks are also described in U.S. PatNo. 5,733,962.

[0095] Also, electrically conductive silica pigments may be used.Examples include AEROSIL 200 sold by Japan Aerosil Co., Ltd., andSYLOID® 161, SYLOID® 244, SYLOID® 308, SYLOID® 404 and SYLOID® 978 allavailable from Fuji Davison Co., Ltd.

[0096] Other electrically conductive pigments can be used, for example,metal powders such as aluminum, copper or special steel, molybdenumdisulphide, iron oxide, e.g., black iron oxide, antimony-doped titaniumdioxide and nickel doped titanium dioxide.

[0097] Also useful are particles coated with metals such as cobalt,copper, nickel, iron, tin, zinc, and combinations of thereof. Suitableparticles which can be coated with the aforementioned metals includealumina, aluminum, aromatic polyester, boron nitride, chromium,graphite, iron, molydenum, neodymim/iron/boron, samarium cobalt, siliconcarbide, stainless steel, titanium diboride, tungsten, tungsten carbide,and zirconia particles. Such metal-coated particles are commerciallyavailable from Advanced Ceramics Corp.

[0098] Other metal-coated particles which may be used advantageously inthe electrodepositable coating composition from which the conductivecoating is deposited include ceramic microballoons, chopped glassfibers, graphite powder and flake, boron nitride, mica flake, copperpowder and flake, nickel powder and flake, aluminum coated with metalssuch as carbon, copper, nickel, palladium, silicon, silver and titaniumcoatings. These particles are typically metal-coated using fluidized bedchemical vacuum deposition techniques. Such metal-coated particles arecommercially available from Powdermet, Inc.

[0099] Mixtures of different electroconductive pigments can be used.

[0100] The conductive pigment is present in the electrodepositablecoating composition in an amount sufficient to provide a conductivecoating having a sufficiently low specific resistance such that a secondelectrodepositable coating (topcoat) may be formed over the conductivecoating as described above. The amount of electroconductive pigment inthe electrodepositable composition can vary depending on the particulartype of pigment that is used, but the level needs to be effective toprovide an electrodeposited coating with a conductivity of greater thanor equal to 10⁻¹² Ohms/centimeter, more typically greater than or equalto 10−¹⁰ Ohms centimeter, and usually greater than or equal to 10−¹⁰Ohms (centimeter).

[0101] In other words, the conductive pigment typically is present inthe first electrodepositable coating composition (apparatus 10) in anamount sufficient to provide an at least partially dried (or cured)coating having a specific resistance of less than 10¹⁰, typicallyranging from 10² to 10¹⁰ Ohms centimeter, such as from 10³ to 10⁸ Ohmscentimeter, e.g., from 10⁴ to 10⁶ Ohms centimeter.

[0102] As discussed above, the electrodepositable coating compositiontypically also contains other pigments to provide corrosion resistance,hiding, or as fillers and additives such surfactants, flow additives andcrater control agents.

[0103] With reference to FIG. 4, after drying and/or curing in the dryer76, the coated blank 84 can be stored for further coating or, moretypically, the coated blank 84 can be directed to one of a plurality ofelectrocoat topcoat stations by a conveyor system 88 so that a topcoatcan be electrodeposited onto the blank 84, e.g., over substantially oneof the major surfaces. As shown in FIG. 4, a plurality of topcoatstations 90, 92, 94 can be positioned downstream of the dryer 76. Eachtopcoat station 90, 92, 94 can have an electrocoat apparatus 96, 98, 100substantially the same as the apparatus 10 described above for applyingthe first, e.g., primer, coating but, as described below, the topcoatelectrocoat apparatus 96, 98, 100 can be slightly modified to apply acontinuous topcoat primarily onto substantially one major surface of theblank 84. The electrocoat tank of each topcoat station 90, 92, 94 can besupplied with the same or a different, e.g., differently colored,(second) coating composition. For example, one topcoat station 90 mayinclude an electrocoat tank having a blue coating composition, anothertopcoat station 92 can have a red coating composition, and a thirdtopcoat station 94 can have a green coating composition.

[0104] For the purposes of explanation only and not to be considered aslimiting, assuming a red topcoat is to be applied to the blank 84 coatedas described above, after exiting the dryer 76 the blank 84 is directedby the conveyor system 88 to the first topcoat station 90. Since theelectrocoat apparatus 96 of the topcoat station 90 is substantially thesame as the apparatus 10 described above, reference will again be madeto FIG. 1 to describe the topcoating procedure conducted at thetopcoating station. The first topcoat station 90 includes an electrocoattank 12 and an electrocoat composition (second composition) as describedabove. However, to apply a topcoat onto a major surface of the blank 84,only one set of electrodes, e.g., only the first or top set ofelectrodes 40, need be present at the second coating region. If thesecond set of electrodes 42 are present, they are may be deenergizedduring the topcoating process described below.

[0105] In the topcoating process, the blank 84 is loaded onto theconveyor 14 and conveyed into the electrocoat tank 12 in similar manneras described above. However, during the topcoating procedure only thefirst set of electrodes 40 are present or energized so that the secondcoating, e.g., a topcoat, is applied onto substantially one majorsurface, i.e. the top major surface, of the blank 84, i.e., the surfaceadjacent the first electrodes 40 in the second coating region. By thephrase “applied onto substantially one major surface” is meant that asubstantially continuous coating is deposited upon one major surfacewhile the majority of the other major surface does not receive thecoating. However, as will be understood by one of ordinary skill in theart, some of the second coating composition may “wrap around” the sidesand onto the bottom major surface of the blank 84 during topcoating. Asdiscussed above, this wrap around effect depends upon several factors,such as the throwpower of the particular coating composition, thetemperature of the coating composition, the impressed voltage and thedwell time of the blank in the electrodeposition bath. As a generalrule, as the throwpower, temperature, voltage, and/or dwell timeincreases, the coverage of the topcoated composition on the bottom sideof the blank 84 will generally increase. In a preferred embodiment, thedeposition parameters are controlled to deposit a substantiallycontinuous topcoat having a thickness of 0.5 mil to 2 mil (0.013 mm to0.05 mm), such as 0.95 mil to 1.3 mil (0.02 mm to 0.03 mm) onto the topmajor surface of the blank 84. The top major surface, therefore, has atotal coating thickness (primer plus topcoat) of 1 mil to 1.5 mil (0.025mm to 0.04 mm).

[0106] The topcoated blank 84 can then be directed through one or morerinse stations 46, 58, drain stations 52, 68, and drying stations 74 insimilar manner as described above to dry and/or cure the applied topcoatcomposition. After drying, the topcoated blank can then be stacked orstored until ready to be shaped into a final, three-dimensional shape,such as a washer or dryer front panel.

[0107] In an alternative embodiment of the invention, the firstconductive coating (primer coating) applied by the apparatus 10 is notdried or cured and the second electrodepositable coating composition(applied at one of the topcoat stations 90, 92, 94) is applied directlyto the non-dried first coating on one major surface of the blank. Thisis generally referred to as a wet-on-wet (“WOW”) application. Awet-on-wet application is typically used where the firstelectrodepositable coating is a transparent or clear coating which issubstantially free of pigment.

[0108] In the embodiment described above, pre-cut, flat metal blanks 84were the substrates being coated. However, the invention is not limitedto use with metal blanks. Metal coils can also be coated using theapparatus and methods described above. However, to coat metal coils, aconveyor 14 as described above is not required. Rather, the coil itselfcan function as the conveyor. For example, the coil can be guided byguide devices, such as wheels or rollers, through the first and/orsecond coating regions to follow the same path described above withrespect to coating metal blanks.

[0109] For coating the coil, the coil can be grounded, i.e., connectedto the electrical power source, outside of the tank 12 in anyconventional manner rather than by an in tank connecting system 26 asdescribed above.

[0110] Upon discharge from the dryer 76, the coil can optionally besheared into blanks at a shearing station 104 (FIG. 4) and the blankstransported to one or more of the topcoat stations as described above.Alternatively, the coil discharged from the dryer 76 can be directed toan inline topcoat station (station 92 in FIG. 4) where a topcoat can beapplied primarily onto one major surface of the coil as described above.The coil can then be sheared into blanks after the topcoat is dried orcured. However, if the coil is first primed and topcoated and thensheared, the blanks will have sheared edges devoid of any protectivecoating. Hence, the method optionally can comprise the additional stepsof applying a conventional corrosion inhibitor such as yttrium acetate,to the sheared edges. Alternatively still, if a topcoat (rather than aprimer and a topcoat as described above) is desired to be applied ontothe substrate, the substrate (whether blank or coil) can be directed toa topcoat station as described above without having a primer applied ina first electrocoat tank.

[0111] As aforementioned, metal blanks coated by the methods of thepresent invention are “post-formed” into parts to be assembled intovarious end-products, for example, front, side and back panels forappliances such as washers, dryers and refrigerators. The post-formingprocesses (e.g., punching and bending) require that the coatings(including the multi-layer composite coatings) which are applied to theblanks be particularly adherent and flexible.

[0112] In one embodiment of the present invention, theelectrodepositable coating composition provides a post-formable coatingcapable of providing a T-bend flexibility rating of less than 6T, oftenranging from OT to 6T, and usually ranging from 2T to 4T as determinedin accordance with ASTM-D4145. In another embodiment of the presentinvention, the electrodepositable coating composition provides apost-formable multi-layer composite coating capable of providing aT-bend flexibility rating of less than 6T, such as ranging from 0T to6T, e.g., from 2T to 4T as determined in accordance with ASTM-D4145.

[0113] Illustrating the invention are the following examples which arenot to be considered as limiting the invention to their details. Unlessotherwise indicated, all parts and percentages in the followingexamples, as well as throughout the specification, are by weight.

EXAMPLES

[0114] It will be appreciated by those skilled in the art that changescould be made to the embodiments described above without departing fromthe broad inventive concept thereof.

[0115] It is understood, therefore, that this invention is not limitedto the particular embodiments disclosed, but it is intended to covermodifications that are within the spirit and scope of the invention, asdefined by the appended claims.

Examples A through B

[0116] The following Examples A and B describe the preparation ofcationic electrodepositable conductive primer compositions useful in theprocesses of the present invention. Example A describes the preparationof pigmented electrodepositable conductive primer coating compositionand Example B describes the preparation of an unpigmentedelectrodepositable conductive primer coating composition. Eachconductive primer composition is in the form of an electrodepositionbath. Each of the electrodeposition bath compositions was prepared byblending under mild agitation the following ingredients: Example AExample B (parts by (parts by Ingredients weight) weight) CR661¹ 1326.331500.00 CP639² 445.82 — Deionized 2027.85 2100.00 Water

[0117] The electrodeposition bath composition of Example A had apigment-to-binder ratio (“p/b”) of 0.15 and a total solids content of17.0 percent based on total weight of the respective electrodepositionbath compositions. The electrodeposition bath composition of Example Bhad a total solids content of 15.0 percent based on total weight of theelectrodeposition bath.

Example 1

[0118] This example describes the preparation of an electrodepositabletop coating composition for application over conductiveelectrodepositable primer compositions in the processes of the presentinvention. The electrodepositable top coating composition is in the formof an electrodeposition bath composition. The electrodeposition bathcomposition was prepared by blending under mild agitation the followingingredients: PARTS BY WEIGHT INGREDIENTS (grams) CR940B¹ 1352.07 CP436²375.88 Deionized water 2072.05

[0119] The resulting electrodepositable top coating bath composition hada total solids content of 15.0 percent based on total bath weight and ap/b of 0.53.

Example 2

[0120] This example describes the powder top coating composition forapplication over conductive electrodepositable primer compositions inthe processes of the present invention. The powder top coatingcomposition is a dry powder coating composition, PCT80139W, commerciallyavailable from PPG Industries, Inc. of Pittsburgh, Pa.

Comparative Example 3

[0121] This comparative example describes application of a conventionalliquid coating system. The liquid coating system was comprised of aliquid urethane primer coating, APPPY 3020, with subsequent applicationof a conventional liquid polyester topcoat, APTW 3952. Both the APPPY3020 and the APTW 3952 are commercially available from PPG Industries,Inc. of Pittsburgh, Pa. The conventional liquid coating compositionswere used as the control series to be evaluated versus theelectrodepositable coating compositions applied by the methods of thepresent invention.

[0122] Test Panel Preparation:

[0123] Each of the above-described electrodepositable conductive primerbath compositions (Examples 1 and 2) was applied to cold rolled steel(“CRS”) test panels, which had been pretreated with CF710 CS20®, a zincphosphate pretreatment composition commercially available from PPGIndustries, Inc.

[0124] The pigmented primer coating of Example A was electrodeposited at15 seconds/1.75 Amps/175 volts onto the zinc phosphated CRS, thenon-pigmented coating Example B was electrodeposited at 60 seconds/1.0Amps/100 Volts. Each primer coating composition was electrodeposited atfilm builds ranging from 0.15 mils to 0.35 mils (3.75 to 8.75micrometers) dry film thickness.

[0125] The electrocoated test panels for Example A were baked at atemperature of 400° F. (204° C.) for 20 minutes to cure the conductiveprimer thereon. The electrocoated test panels for Example B were then“flashed” for 5 minutes at room temperature to allow dehydration tooccur.

[0126] The electrodepositable top coating composition of Example 1 wasthen applied to the primed test panels prepared as described immediatelyabove. For Example A, (cured conductive primer), and Example B,(air-dried conductive clear coat), the electrodepositable top coatingcomposition of Example 1 was electrodeposited at 90 seconds/1.2 Amps/125Volts. The top coated panels thus prepared were then baked at atemperature of 350° F. (177° C.) for 20 minutes to cure theelectrodepositable top coating composition. The cured top coatingcompositions had a dry film thickness ranging from 1.20 to 1.4 mils (30to 35 micrometers).

[0127] The powder top coating composition of Example 2 was then appliedto the primed test panels. For Example A (cured conductive primer), andExample B (air-dried conductive clear coat), the powder topcoatcomposition of Example 2 was applied by electrostatic spray. The topcoated panels thus prepared were then baked at a temperature of 400° F.(204° C.) for 10 minutes to cure the powder topcoat. The cured powdertopcoat composition had a dry film thickness ranging from 1.20 to 2.20mils (30 to 55 micrometers).

[0128] With respect to the conventional liquid coating system of Example3, the primer APPY 3020 was roll applied to zinc phosphate treatedgalvanized steel substrate, then cured at a temperature of 400° F. (204°C.) for 10 minutes. A dry film thickness of 0.2 mils (5 micrometers) wasachieved. The liquid topcoat was then spray applied to the primedsubstrate and cured at a temperature of 400° F. (204° C.) for 10 minutesto form a topcoat having a dry film thickness of 0.8 mils (20.3micrometers).

[0129] The test panels thus prepared were evaluated for corrosionresistance by salt spray testing in accordance with ASTM B17; detergentresistance in accordance with ASTM D2248; and flexibility by T Bendtesting in accordance with ASTM D4145. (where 0T=best; np represents nocoating pick off; and nc represents no chipping.)

[0130] Test results are reported below in the following TABLE 1. TABLE 1Salt Spray Conductive Flexible Corrosion Detergent Primer Top CoatResistance Resistance Flexibility Example A Example 1 1.5 mm total Noblisters 2T np 3T nc scribe creepage Example B Example 1 3.0 mm totalFew #8 3T np/nc scribe creepage blisters Example A Example 2 0.5 mmtotal No blisters 3T np/nc scribe creepage Example B Example 2 0.5 mmtotal Medium #8 2T np/nc scribe creepage blisters Not Example 3   2 mmtotal < few #8 4T np/nc applicable (compara- scribe creepage blisterstive)

[0131] The data presented in Table 1 illustrate that the two coatprocess of the present invention provides flexibility properties, 2T npand 1T nc better than the comparative prepaint control system applied byconventional processes. The two coat systems of the present inventionusing Example A as the primer and Examples 1 and 2 as the flexibletopcoats provides better detergent and salt spray performance thanExample 3, the comparative prepaint system applied by conventionalprocesses.

[0132] It will be appreciated by those skilled in the art that changescould be made to the embodiments described above without departing fromthe broad inventive concept thereof. It is understood, therefore, thatthis invention is not limited to the particular embodiments disclosed,but it is intended to cover modifications which are within the spiritand scope of the invention, as defined by the appended claims.

We claim:
 1. A continuous electrocoat apparatus for applying a coatingonto at least a portion of a substantially flat substrate having twomajor surfaces, the apparatus comprising: a first electrocoat tank; atleast one first electrode spaced from at least one second electrode anddefining a first coating region to apply a first aqueouselectrodepositable coating composition onto both major surfaces of thesubstrate between the first and second electrodes; a second electrocoattank located downstream of the first electrocoat tank; and at least onethird electrode located in the second electrocoat tank and defining asecond coating region adjacent the third electrode to apply a secondaqueous electrodepositable coating composition onto substantially onemajor surface of the substrate.
 2. The apparatus as claimed in claim 1,including a conveyor extending through the first coating region anddefining a first conveyor path, with the first and second electrodeslocated on opposed sides of the first conveyor path.
 3. The apparatus asclaimed in claim 2, including a connecting system configured to apply anelectric potential to the substrate in the coating region.
 4. Theapparatus as claimed in claim 3, wherein the conveyor comprises aplurality of electrically conductive supports configured to contact thesubstrate and the connecting system is configured to provide electricityto at least a selected portion of the supports in the first coatingregion.
 5. The apparatus as claimed in claim 4, wherein the conveyorcomprises a plurality of non-conductive members, with the supportscarried on the non-conductive members.
 6. The apparatus as claimed inclaim 1, wherein the substrate is a metal coil and the apparatusincludes a guide device to guide the coil through the first coatingregion.
 7. The apparatus as claimed in claim 2, wherein the conveyorincludes at least one holding element configured to bias the substratetoward the conveyor.
 8. The apparatus as claimed in claim 6, wherein theguide device includes a roller.
 9. The apparatus as claimed in claim 4,wherein the connecting system includes: a bus bar located adjacent thefirst electrocoat tank; and a plurality of grounding bars carried on theconveyer, with each grounding bar connected to at least one support, andwith each grounding bar having an outer and configured to contact thebus bar when the grounding bar is in the coating region.
 10. Theapparatus as claimed in claim 1, wherein the first coating compositionis different than the second coating composition.
 11. The apparatus asclaimed in claim 10, wherein the first coating composition is acorrosive-resistant coating composition.
 12. The apparatus as claimed inclaim 10, wherein the second coating composition is an appearanceenhancing coating composition.
 13. The apparatus as claimed in claim 1,wherein the coating formed by the first and second coating compositionshas a T-bend rating in the range of 0 to 6T.
 14. A continuouselectrocoat apparatus for applying a coating onto at least a portion ofa substantially flat substrate, the apparatus comprising: a firstelectrocoat tank having a coating region; a non-conductive conveyorextending at least partially into the first electrocoat tank anddefining a conveyor path; a plurality of electrically conductivesupports carried on the conveyor; a connecting system configured toprovide an electric potential to at least a selected portion of thesupports when the selected portion of the supports are in the coatingregion of the first electrocoat tank; and a plurality of firstelectrodes positioned in the first electrocoat tank, with the firstelectrodes located on a first side of the conveyor path.
 15. Theapparatus of claim 14, wherein the conveyor is a closed-loop conveyor.16. The apparatus of claim 14, wherein the conveyor comprises aplurality of non-conductive chains.
 17. The apparatus of claim 14,wherein the conveyor includes holding elements configured to bias thesubstrate toward the conveyor.
 18. The apparatus of claim 17, whereinthe holding elements comprise magnets spaced from an outer surface ofthe conveyor.
 19. The apparatus of claim 14, wherein the supports extendbeyond an outer surface of the conveyor.
 20. The apparatus of claim 14,wherein the supports are tapered.
 21. The apparatus of claim 16, whereinthe chains are laterally spaced from one another and the supports onadjacent chains are aligned to define rows of supports on the conveyor.22. The apparatus of claim 21, wherein each chain moves at substantiallythe same speed to maintain the rows of supports as the conveyor moves.23. The apparatus of claim 14, including a connecting system configuredto connect the supports in the coating region with an electrical powersource.
 24. The apparatus of claim 23, wherein the connecting systemincludes a bus bar located adjacent the electrocoat tank.
 25. Theapparatus of claim 24, wherein the bus bar is located above theelectrocoat tank.
 26. The apparatus of claim 24, wherein the connectingsystem includes a plurality of grounding bars, with each grounding barconnected to at least one support, and with each grounding bar having anouter end configured to contact the bus bar when the supports to whichthe grounding bar are connected are in the coating region.
 27. Theapparatus of claim 14, wherein the first electrodes are located abovethe conveyor path in the electrocoat tank.
 28. The apparatus of claim14, including a plurality of second electrodes located on a side of theconveyor path opposite to the first electrodes.
 29. The apparatus ofclaim 28, including at least one second electrocoat tank locateddownstream of the first electrocoat tank and having a second electrocoatconveyor extending at least partially into the second electrocoat tankand defining a second conveyor path, wherein the second tank includes aplurality of third electrodes located on one side of the second conveyorpath.
 30. The apparatus of claim 29, wherein the second electrocoat tankincludes a plurality of fourth electrodes located on a side of theconveyor path opposite to the third electrodes.
 31. A continuouselectrocoat apparatus for applying a coating over at least a portion ofa substantially flat substrate, the apparatus comprising: a firstelectrocoat tank having a coating region; a non-conductive conveyorextending at least partly into the first electrocoat tank and defining aconveyor path, the conveyor comprising a plurality of laterally spaced,non-conductive chains movably mounted on rotatable members such that thechains move at substantially the same speed; a plurality of electricallyconductive supports carried on each chain to form a support surface ofthe conveyor; a plurality of grounding bars carried on the conveyor,with each grounding bar connected to at least one support; a bus barlocated adjacent the electrocoat tank, wherein the bus bar is configuredto contact one or more grounding bars carried on a portion of theconveyor in the coating region of the first electrocoat tank.
 32. Amethod for applying a coating onto at least a portion of a substantiallyflat substrate having two major surfaces, comprising the steps of: (a)conveying the substrate between at least one first electrode and atleast one second electrode in a first coating region to apply a firstaqueous electrodepositable coating composition onto both major surfacesof the substrate; (b) conveying the substrate adjacent at least onethird electrode located in a second coating region to apply a secondaqueous electrodepositable coating composition onto substantially onemajor surface of the substrate.
 33. A method as claimed in claim 32,including drying the coating applied in step (a) before applying thecoating of step (b).
 34. A method as claimed in claim 32, wherein thesubstrate is a metal blank.
 35. A method as claimed in claim 32, whereinthe substrate is a metal coil.
 36. A method as claimed in claim 32,wherein the first coating composition is different from the secondcoating composition.
 37. A method as claimed in claim 36, wherein thefirst coating composition is a primer composition.
 38. A method asclaimed in claim 36, wherein the second coating composition is anappearance enhancing composition.
 39. A method of electrocoating asubstantially flat substrate having two major surfaces, comprising thesteps of: placing the substrate onto a non-conductive conveyor having aplurality of conductive supports defining a support surface, theconveyor defining a conveyor path through a coating region of anelectrocoat bath; applying an electric potential to the substrate whenthe substrate is in the coating region; conveying the substrate throughthe coating region adjacent at least one electrode to apply an aqueouselectrodepositable coating composition onto at least one major surfaceof the substrate; and drying the coated substrate at a drying stationlocated downstream of the electrocoat bath.
 40. The method of claim 39,wherein the electrocoat bath includes at least one first electrodelocated on one side of the conveyor path and at least one secondelectrode located on an opposite side of the conveyor path and themethod includes moving the substrate between the first and secondelectrode to apply the coating composition to both major surfaces of thesubstrate.
 41. The method of claim 40, including moving the substrate ata speed such that the substrate has a dwell time of 5 secs to 30 secs inthe coating region.
 42. The method of claim 39, wherein the electricalpotential is applied to the substrate by supplying electrical power tothe conveyor supports in the coating region.
 43. The method of claim 42,wherein the electrical power is supplied by contacting a grounding barattached to at least one support in the coating region with a bus barlocated adjacent the coating tank.
 44. The method of claim 40, includingapplying the coating composition such that the dried coating has athickness of 0.004 mm to 0.006 mm on both major surfaces of thesubstrate.
 45. The method of claim 40, including directing the coatedsubstrate to a topcoat station having a second electrocoat bath with asecond conveyor defining a second conveyor path through a coating regionof the second electrocoat bath, wherein the second electrocoat bathincludes at least one third electrode located on one side of the secondconveyor path and the method includes moving the coated substrate pastthe third electrode to apply a topcoat composition onto a major surfaceof the substrate.
 46. The method of claim 45, including drying thetopcoat composition.
 47. The method of claim 46, including applying thetopcoat composition such that the dried topcoat has a thickness of 0.02mm to 0.03 mm.
 48. A continuous electrocoat apparatus for applying acoating onto at least a portion of a substantially flat substrate havingtwo major surfaces, the apparatus comprising: means for conveying thesubstrate between at least one first electrode and at least one secondelectrode in a first coating region to apply a first aqueouselectrodepositable coating composition onto both major surfaces of thesubstrate; and means for conveying the substrate adjacent at least onethird electrode located in a second coating region to apply a secondaqueous electrodepositable coating composition onto substantially onemajor surface of the substrate.
 49. A continuous electrocoat apparatusfor applying a coating onto at least a portion of a substantially flatsubstrate having two major surfaces, the apparatus comprising: means forplacing the substrate onto a non-conductive conveyor having a pluralityof conductive supports defining a support surface, the conveyor defininga conveyor path through a coating region of an electrocoat bath; meansfor applying an electric potential to the substrate when the substrateis in the coating region; means for conveying the substrate through thecoating region adjacent at least one electrode to apply an aqueouselectrodepositable coating composition onto at least one major surfaceof the substrate; and means for drying the coated substrate at a dryingstation located downstream of the electrocoat bath.